The invention concerns a process and a device to operate a warp knitting machine, in particular a stitch-bonding machine with knitting elements, the knitting needles of which pierce a continuously fed fabric web and thereby carry out the knitting process.
A machine of this kind, used in addition to knit weft yarns into the finished fabric, is described in German Offenlegensschrift No. 2 316 160. The weft yarns are, in this case, conveyed to the knitting elements by means of a conveyor driven at uniform speed. This also applies to the band of material which advances constantly at the same speed.
In this type of operation, the knitting needles interrupt the continuous conveying of the band of material for as long as they are pierced into same. If the distance from one knitting stitch to the next knitting stitch is relatively long, this can lead to a jamming of the band of material.
Furthermore, the European patent application No. 0 018 766 discloses a stitch-bonding machine to which a fiber fleece is fed, constituting the band of material, whereby the fleece is held up for as long as it is pierced by the needles. However, this requires a corresponding, step-by-step manner of driving the fleece, and this is again undesirable because it can cause irregularities in the goods produced.
It is the object of the instant invention to solve these problems. According to the invention this is accomplished by superimposing a transversal movement to the movement of the knitting needles, parallel to the direction of advance of the band of material, lasting from the moment of their introduction into the material to the moment of their exiting the material, of such nature as to cause the knitting needles to follow the band of material essentially at the speed of the band of material for as long as they are in contact with said band of material, and to cause said needles to be brought back, at an offset position in relation to the band of material, to their starting position before their introduction into the material again.
Because of this superimposed movement of the knitting needles, the latter exert no pull on the continuously conveyed band of material, neither against nor in the direction of advance, resulting in a particularly smooth operation and making it possible to obtain without difficulty, longer distances between stitches, in the direction of advance.
The imparting of swivelling movement counter to the running direction to the knitting needles and to the yarn guides in order to reduce the forces of acceleration in a warp knitting machine in which no band of material is fed, so that the relative movement remains the same in its effect, whereby each attributed bar, however, has to execute a correspondingly shortened movement, is known from German Patentschrift No. 1 585 173. The movement of the knitting needles in this case is such that as they rise, they do not carry out any advance movement, so that a corresponding pull is exerted by the knitted band of material upon the knitting needles due to the draw-off of the fabric as the needles rise. Also, while the knitting needles descend, they are moved in the direction opposite to the draw-off movement of the knitted band of material, thus obviously further increasing the pull exerted by the band of material upon the knitting needles. If this principle of movement were to be transferred to a stitch-bonding machine, it would result in a pull in a direction opposite to the advance of the conveyed band of material and this would interfere considerably with the stitch-bonding process.
German Patentschrift No. 1 585 238 discloses an application of the above-described principle of relative movement to a warp knitting machine provided with a trace comb and operating without a band of material being presented, whereby the trace comb can be held free of motion. The movement of the knitting needles, in this case, takes place in principle as described above for German Patentschrift No. 1 585 173, whereby the range movement of the knitting needles, however counter to the direction of draw-off, is shortened. In case of application of this principle to a warp knitting machine with conveyed band of material, the up and down movement of the knitting needles would be accompanied by a stoppage of the band of material in every instance.
Aside from the fact the neither German Patentschrift No. 1 585 173 nor German Patentschrift No. 1 585 238 contain any reference to stitch-bond knitting in connection with a represented band of material, it should be pointed out that the sequences of movement disclosed in both patent publications are unsuitable for stitch-bonding machines.